Since the early 1980s, adjustable gastric bands have provided an effective alternative to gastric bypass and other irreversible surgical weight loss treatments for the morbidly obese. The gastric band is wrapped around an upper portion of the patient's stomach, forming a stoma that restricts food passing from an upper portion to a lower portion of the stomach. When the stoma is of the appropriate size, food held in the upper portion of the stomach provides a feeling of fullness that discourages overeating. However, initial maladjustment or a change in the stomach over time may lead to a stoma of an inappropriate size, warranting an adjustment of the gastric band. Otherwise, the patient may suffer vomiting attacks and discomfort when the stoma is too small to reasonably pass food. At the other extreme, the stoma may be too large and thus fail to slow food moving from the upper portion of the stomach, defeating the purpose altogether for the gastric band.
An artificial sphincter may be utilized in any number of applications within a patient's body where it is desirable to vary the size of an orifice or organ. Depending upon the application, artificial sphincters may take the form of a flexible, substantially non-extensible band containing an expandable section that is capable of retaining fluids. The expandable section would be capable of expanding or contracting, depending upon the volume of fluid contained therein. One particular example of an artificial sphincter is an adjustable gastric banding device, such as described in U.S. Pat. Nos. 4,592,339, 5,226,429, 6,102,922, and 5,449, 368, the disclosure of each being hereby incorporated by reference. Adjustable gastric band implants have a hollow elastomeric balloon with fixed end points encircling a patient's stomach just inferior to the esophago-gastric junction. When saline solution is delivered into the hollow balloon, the gastric band swells and constricts the stomach, for example, for obesity reduction. Different degrees of constriction are desired, and adjustment is required over time as the patient's body adapts to the constriction.
Adding or removing saline solution from the adjustable gastric band is typically accomplished by injection through a fluid injection port to achieve a desired diameter. Since adjustable gastric bands may remain in the patient for long periods of time, the fluid injection port is typically installed subcutaneously to reduce the likelihood of infection. Adjusting the amount of fluid in the adjustable gastric band is achieved by inserting a Huber tip needle through the skin into a silicon septum of the injection port. Once the needle is removed, the septum seals against the hole by virtue of compressive load generated by the septum. A flexible conduit communicates between the injection port and the adjustable gastric band.
While subcutaneously implanted injection ports are a successful approach to readily adjusting a gastric band, and are a desirable feature to retain for initial installation or as a backup, it would be desirable to remotely adjust the gastric band. Although minimally invasive, insertion of the Huber needle to adjust the saline solution volume does introduce increased risk of infection. In addition, this procedure typically entails the inconvenience and expense of scheduling time with a surgeon.
Incorporating remote control of an implanted artificial sphincter would be desirable; however, adjustable gastric bands such as those described above are currently fabricated out of material that does not pose significant limitations on the patient. In particular, increasingly Magnetic Resonance Imaging (MRI) is used as a diagnostic tool and as an aid in performing minimally invasive surgical procedures. MRI operates by creating a strong DC magnetic field (e.g., 0.5-1.5 Teslas) and then disturbing the DC magnetic field with magnetic impulses that induce a weak radio frequency (RF) signal to be emitted by the tissue of a patient. Thus, it is desirable that implantable medical devices contain no ferrous material that would be attracted by the strong DC magnetic field. Otherwise, tissue damage, patient discomfort, or malfunction of the implantable medical device may occur. Further, it is desirable that the medical device not interfere with the weak radio frequency that is produced by the patient, or else artifacts may be created in the diagnostic image that degrade its value.
Efforts have been made to produce other types of implantable devices with actuators that can endure the environment of an MRI machine to some degree. For example, it is known to implant a drug dispensing infuser pump that operates with an electrical DC motor. The deleterious effects of magnetizing the ferrous materials of the DC motor therein is countered by a degree by over-building the device such that operation may continue in a degraded condition. Further, the size of the structural attachments to the DC motor have to be greatly increased to withstand the magnetic attraction that the MRI machine imposes, as well as avoid tissue damage and discomfort by increasing the overall size of the implant, which is not otherwise a desirable design constraint.
It is also known to incorporate MRI safe devices such as a piezoelectric motor into an peristaltic pump, also for drug dispensing. However, peristaltic pumps are unsuitable for long-term intermittent bi-directional fluid control. Even modest leakage past the peristaltic pump during inactive periods would prove unsuitable for fluid control of implants.
Consequently, a significant need exists for a remotely controllable implantable artificial sphincter apparatus that would be MRI safe.